Altered gait patterns resulting from amputation has been implicated as a possible mechanism for early degenerative changes in the sound limb of unilateral amputees. The purpose of this study was to examine the ground reaction force characteristics and joint motion in this population. Ground reaction forces, joint motion, and stride characteristics of 10 traumatic below-knee amputees were analyzed while wearing five different prosthetic feet (SACH, Flex-foot, Carbon Copy II, Seattle, and Quantum). Subjects used each foot for 1 month prior to testing. Results indicated that the Flex-foot significantly reduced the initial peak of the vertical ground reaction force on the sound limb compared to all other feet tested (p < .0001). The SACH foot consistently produced the greatest ground reaction forces on the sound limb; however, this was not statistically significant. The effective factor of the Flex-foot appears to be minimization of the center of gravity elevation, which was accomplished through a significant increase in terminal stance dorsiflexion compared to the other feet tested (p < .0001).